Method of increasing covering power of knitted cotton fabric

ABSTRACT

Yarns in knitted cotton or other cellulosic fabric are subjected to modification of cross-sectional dimensions through the use of press rollers and are immediately thereafter cross-linked thereby durably increasing the covering power (as measured by airpermeability) and/or the opacity of the treated fabric.

United States Patent [191 Frick, Jr, et al.

METHOD OF INCREASING COVERING POWER OF KNITTED COTTON FABRIC Inventors: John G. Frlck, Jr.; Gloria A.

Gautreaux, both of New Orleans, La.

The United States of America as represented by the Secretary of Agriculture, Washington, DC.

Filed: Sept. 13, 1972 Appl. N0.: 288,806

Assignee:

US. Cl 8/ll5.5, 8/185, 8/187, 38/144 Int. Cl. D06c 15/00 Field of Search 38/144; 8/184, 185, 187, 8/1 15.5

References Cited UNITED STATES PATENTS 6/1968 Tewksbury et al. 8/184 X Nov. 19, 1974 3,650,671 3/1972 Bergmann ..8/l84 3,754,860 8/1973 Frick et al. 8/184 X OTHER PUBLICATIONS Crease Resisting Fabrics, J. T. Marsh, Reinhold Publ. Co., NY. 1962, PP- 167-169, & 1.96-202.

Primary Examiner-Stephen J. Lechert, Jr.

2 Claims, No Drawings METHOD OF INCREASING COVERING POWER OF KNITTED COTTON FABRIC A non-exclusive, irrevocable, royalty-free license in the invention herein described throughout the world for all purposes of the United States Government, with the power to grant sublicenses for such purposes, is

hereby granted to the Government of the United States.

This invention relates to physical treatment of knitted cellulosic fabric followed by chemical treatment in order to retain the desired newly established yarn dimensions. More specifically, this invention relates to a method of processing knitted cotton and other cellulosic fabrics wherein by subjecting the knitted fibrous cellulosic structure to pressure from press rollers a dis placement of the fibers in the yarns is caused physically and permanently maintained upon subjecting the fabrictherefore the yarns of the new cross-sectional dimensions-to chemical crosslinking. The finished products have an imparted lower air-permeability and increased opacity which renders the finished garment or other goods more serviceable in that greater covering power is had for the same or lesser weight of cellulosic material which would be required in prior fabric construction.

DEFINITIONS Covering power is a term employed throughout this specification to signify the ability of the knitted material to shield a person or material from the environment. For purposes of this specification the said covering power is measured by ASTM Test Method 0737-69 using the permometer which measures air permeability.

Opacity is a term correlated to covering power in that having the one caused the other to be there also. Opacity" as used in this specification deals with the ability to obstruct the view but not the passage of air. The test here is simply the subject approach of being able to see or not to see through a knitted fabric.

BACKGROUND OF THE INVENTION This invention provides a means of obtaining increased opacity without knitting a special textile construction which would require more cotton or other cellulosic yarn per unit area, and which would be more difficult to knit therefore more time consuming and less economical.

In most uses fabric is intended to form an opaque cover or screen. It has been felt that this screen should allow the passage of air and should not be a solid sheet. In any event, the methods of producing fabric, by knitting or weaving, are inherently incapable of producing a solid film. It is particularly difficult in knitting to place the adjacent yarns close enough together to make the fabric sufficiently opaque for many uses. Because of the expense of knitting fabric with sufficient opacity, knitted fabric has been avoided in some uses.

It has been possible with fabric composed of synthetic, thermoplastic fibers to increase opacity after knitting. The fabric is pressed at temperatures above the softening point of the fiber. The yarns are flattened and spread into the spaces between yarns. Opacity is increased because the open areas between yarns is decreased. As the yarn cools it resets or fixes itself in the new shape. With cotton, however, this process is not possible. Because cotton is not thermoplastic, the change in shape imparted to the yarns is not permanent. Transparency returns on use and laundering.

The main object of this invention is to provide a method of processing cotton and other cellulosic fab- .rics which have been loosely knitted so that by combining physical and chemical forces an easily knitted fabric is converted to a finished knitted fabric with high opacity and high covering power achieved through the use of available machinery and chemicals.

In general, this invention consists of l) selecting a relatively loose, easily knitted cotton or other cellulosic fabric which has poor opacity and subjecting said fabric to pressure by passing the fabric through squeeze rolls to reduce the interyarn spaces as the yarns move to the vacant spaces within the structure of the knitted fabric, and (2) applying a selected crosslinking agent to secure chemically what has been shaped physically.

The processing is carried out in this manner. To the knitted fabric is first applied a solution of crosslinking agent for cellulose which is the primary chemical component of cotton. The wet impregnated fabric is then passed through press rollers under sufficient pressure to spread the yarn to unoccupied spaces within the fabric structure without reducing the strength of the fabric. The spreading of the yarn causes it to occupy more space laterally and partially fill the interyarn spaces. The open areas contributing to transparency are thereby reduced. With the fabric still in the imparted shape reaction between cellulose and the crosslinking agent is promoted by heating in the presence of a catalyst. This crosslinking prevents motion among molecules and larger elements within the fiber and the fiber is locked in the shape it has at time of reaction.

With the fibers so fixed the yarn is restrained from returning to its original shape from the spread shape. As a result, the decrease in transparency or increase of opacity is retained to a useful extent through use and laundering.

PREFERRED EMBODIMENTS The method of this invention is applicable to knitted fabrics made of cotton and other cellulosic fibrous material in which the yarns are not so tightly twisted and hard that they cannot be spread under pressure. In principle the invention is also applicable to other fabrics that are composed mainly of cellulose.

The crosslinking agent for the cellulose is preferably one of those that are used to introduce wrinkle resistance, wash-wear, and durable-press properties into cellulose fabrics. They are commonly the polymethylolamides or poly-N-hydroxymethyl derivatives of organic amides. Examples of these are dimethylol ethyleneurea, dimethylol propyleneurea, dimethylol dihydroxy ethyleneurea, dimethylol methyl carbamate, and tetramethylol acetylenediurea. These agents are preferred because they react readily with cellulose with only brief heating in the presence of a catalyst and the crosslinks they produce are durable to launder. Typical catalysts for use with these agents are acidic salts, such as zinc nitrate, zinc chloride, magnesium chloride, and ammonium chloride.

The crosslinking agent is applied to the knitted fabric by impregnation with an aqueous solution containing 5 to 15 percent crosslinking agents, 0.5 to 3.0 percent catalyst, and, if desired, other additives commonly used in finishing to give the fabric a 60-100 percent weight gain. Common additives are lubricants, such as polyethylene, that aid sewing of the treated fabric and hand-builders, such as polyvinyl alcohol, that give a firm hand and increase abrasion resistance. Preferably the fabric is soaked in the formulation solution and passed through squeeze rolls to bring the amount of solution on the fabric within the desired range and to give an even distribution of chemicals; however, other methods of application, such as spraying, back coating, or soaking and centriguation can be employed.

After the impregnation the fabric is subjected to a drying step to lower the moisture content. This can be done by heating the impregnated fabric at 50100C, temperatures low enough to avoid the reaction of the fabric with the crosslinking agent. The purpose of this step is to reduce the moisture content so that no solution is expressed on subsequent squeezing. The fabric is then passed between metal rolls that exert a pressure of about 0.1 to 0.5 tons per centimeter of roll width. The temperature of the metal rolls is maintained at about 100-1 C. One or two passes through the rolls are sufficient. Calender rolls, which are commonly employed to impart a gloss or a smooth surface on woven fabrics have been employed satisfactorily. The fabric is finally heated to a high enough temperature, 140-180C for 2-4 minutes, to cause reaction of the crosslinking agent as soon as possible after pressing and before washing to maintain the imparted configuration of the fibers and yarns; thence the fabric may be washed with only partial loss of the increased opacity or covering power.

The knitted cotton fabrics which were treated by the method of this invention attained increased opacity and retained some permeability. Ordinarily, the air permeability of the cotton knitted fabrics is reduced to onehalfof its original value. It must be noted that impermeability is neither desired nor achieved by the method of this invention. Among the desirable qualities that are imparted are the following: improved ability to dry smoothly, wrinkle resistance, and increased dimensional stability.

The following examples are provided to illustrate mainly the preferred embodiments of this invention and should not be construed as limiting the invention in any manner whatever. The percentages have references to weight quantities. Fabric properties were determined by methods currently recommended by the American Society for Testing Materials and the American Association of Textile Chemists and Colorists.

EXAMPLE 1 A cotton fabric, knitted in a cobblestitch pattern with 10 wales and 13 courses per centimeter and weighing 176 g/square meter, is wet with a solution of 6 percent dimethylol dihydroxyethyleneurea, 0.6 percent zinc nitrate hexahydrate, 0.5 percent emulsified polyethylene, and 3 percent low molecular weight polyvinyl alcohol. The wet fabric is padded and dried at 60C for 10 minutes while it is held smooth on a frame. The dried fabric is then passed twice through calender rolls at 3 meters per minute. The calender rolls were 30 cm long, were forced together with 5 tons force, and were heated to 100C. After calendering the fabric was heated 3 minutes at 160C.

The treated fabric after 5 launderings had an air permeability of 3.6 cu.m./min./sq. cm. The original untreated fabric had an air permeability of 8.2 cu.m.-

/min./sq. m, and fabric treated with crosslinking agent to reduce shrinkage and raise durable-press rating only had an air permeability of 8.9 cu.m./min./sq. m. after 5 launderings. Visual examination of the treated fabric confirmed the high opacity indicated by air permeability. Bursting strength was reduced from 7.24 kg./sq. cm. to 3.52 kg./sq. cm. by the treatment. This reduction in strength is the same as that caused by the treatment for increased durable-press rating and decreased shrinkage only.

EXAMPLE 2 Samples of a cotton fabric knitted in a honeycomb pattern with 11 wales and 13 courses per centimeter and weighing about 139 g./sq. m. are padded with one of the following solutions:

Solution 1: 6 percent dimethylol dihydroxyethyleneurea, 2.5 percent magnesium chloride hexahydrate, and 0.5 percent emulsified polyethylene.

Solution 11: 6 percent dimethylol dihydroxyethyleneurea, 2.5 percent magnesium chloride hexahydrate, 0.5 percent emulsified polyethylene, and 3 percent low molecular weight polyvinyl alcohol.

The padded samples of fabric were dried 10 minutes at 60C and then passed twice through a calender at 3 m. per min. The calender had 30 cm. rolls that were forced together by 4-5 tons and were heated to C. The fabrics were heated at 160C for 3 minutes and then washed. The treated fabric at this stage and after 5 more launderings were compared with the untreated fabric.

Air permeability The treated fabrics had reduced air permeability indicating greater opacity, most of which persisted through 5 launderings.

We claim:

I. A method for increasing the opacity and covering power of a cellulosic knitted fabric comprising impregnating said fabric with a cross-linking agent, passing the impregnated fabric through press rollers which are heated to about 100 C. to C. and which exert a pressure on said fabric of about 0.1 to 0.5 tons per centimeter of roll widths, and reacting the cross-linking agent with said fabric after passing the fabric through said rollers.

2. A process for increasing the opacity and covering power of a loosely-knit fibrous cellulosic fabric, comprising:

a. impregnating said fabric with a cellulose crosslinking formulation containing a cellulose crosslinking agent and an agent for catalyzing crosslinking between the cellulose of the fabric and the crosslinking agent;

b. subjecting the impregnated fabric to sufficient pressure to deform the cross-sectional dimensions of its fibers and yarns and impart a new configuration thereto in which the yarns partially fill the interyarn spaces and occupy more space laterally than did the corresponding original yarns; and

c. heating the thus-deformed fabric to effect crosslinking in the cellulose of the fabric thereby to permanently fix the said new configuration in the fabnc *k l 

1. A METHOD FOR INCREASING THE OPACITY AND COVERING POWER OF A CELLULOSIC KNITTED FABRIC COMPRISING IMPREGNATING SAID FABRIC WITH A CROSS-LINKING AGENT, PASSING THE IMPREGNATED FABRIC THROUGH PRESS ROLLERS WHICH ARE HEATED TO ABOUT 100*C TO 110*C. AND WHICH EXERT A PRESSURE ON SAID FABRIC OF ABOUT 0.1 TO 0.5 TONS PER CENTIMETER OF ROLLS WIDTHS, AND REACTING THE CROSS-LINKING AGENT WITH SAID FABRIC AFTER PASSING THE FABRIC THROUGH SAID ROLLERS.
 2. A process for increasing the opacity and covering power of a loosely-knit fibrous cellulosic fabric, comprising: a. impregnating said fabric with a cellulose cross-linking formulation containing a cellulose crosslinking agent and an agent for catalyzing crosslinking between the cellulose of the fabric and the crosslinking agent; b. subjecting the impregnated fabric to sufficient pressure to deform the cross-sectional dimensions of its fibers and yarns and impart a new configuration thereto in which the yarns partially fill the interyarn spaces and occupy more space laterally than did the corresponding original yarns; and c. heating the thus-deformed fabric to effect cross-linking in the cellulose of the fabric thereby to permanently fix the said new configuration in the fabric. 